YorkSpace
York University's Institutional Repository
    • English
    • français
  • English 
    • English
    • français
  • Login
View Item 
  •   YorkSpace Home
  • Faculty of Graduate Studies
  • Electronic Theses and Dissertations (ETDs)
  • Biology
  • View Item
  •   YorkSpace Home
  • Faculty of Graduate Studies
  • Electronic Theses and Dissertations (ETDs)
  • Biology
  • View Item
JavaScript is disabled for your browser. Some features of this site may not work without it.

Circadian Rhythm in Intrinsic Heart Rate

Thumbnail
View/Open
Barazi_Nour_2020_Masters.pdf (2.291Mb)
Date
2020-11-13
Author
Barazi, Nour

Metadata
Show full item record
Abstract
Heart rate (HR) as well as adverse cardiac events (i.e. myocardial infarction, arrhythmias, stroke, and sudden cardiac death) show circadian patterns. Circadian HR fluctuations are traditionally thought to be controlled by the autonomic nervous system (ANS). However, recent studies have concluded that diurnal HR variation arise from intrinsic remodeling in SA node. To re-examine the mechanisms controlling circadian HR fluctuations, we performed surface electrocardiographic recordings (sECG) at 4 time points per day (ZT0, ZT6, ZT12 and ZT18) in CD1 mice that had been anesthetized in order to eliminate the potential confounding effects of activity on daily HR variation. We found that unconscious mice still showed diurnal HR fluctuation with peaks of HR in the dark period (ZT 18) and HR troughs in the light period (ZT 6). The amplitude of circadian HR fluctuations was reduced by ~2/3 by blockade of the cardiac parasympathetic nervous activity (PNA) with atropine while being reduced by ~1/3 by blockade of the cardiac sympathetic nerve activity (SNA) with propranolol. Complete ANS block abolished entirely the diurnal HR fluctuations. To assess the contribution of activity to diurnal HR fluctuations we also analyzed HR in telemetrized sedentary mice which showed, unexpectedly, nearly identical amplitudes of HR fluctuations to anesthetized mice. On the other hand, after mice were given access to running wheels for 1 week, the circadian HR amplitudes increased by ~150%. Conclusion: HR fluctuation requires the ANS even in the absence of physical activity with a 2:1 proportion of parasympathetic versus sympathetic control of circadian rhythm in basal HR. These results highlight the importance of taking experimental time of day into consideration when assessing HR responses to treatments and drug administration in anesthetized mice.
URI
http://hdl.handle.net/10315/37958
Collections
  • Biology

All items in the YorkSpace institutional repository are protected by copyright, with all rights reserved except where explicitly noted.

YorkU LogoContact Us | Send Feedback
Sitemap for search engines

 

Browse

All of YorkSpaceCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

My Account

LoginRegister

Statistics

View Usage Statistics

All items in the YorkSpace institutional repository are protected by copyright, with all rights reserved except where explicitly noted.

YorkU LogoContact Us | Send Feedback
Sitemap for search engines